A Study of a Weakly Ionized Rotating Plasma

Measurements are reported on a weakly ionized rotating argon plasma generated by two identical gas discharges facing each other. In each discharge a current up to 100 A is drawn between a point-like cathode and a ring-shaped anode. Axial magnetic fields up to 0.26 T are applied. All measurements have been done at 1 torr. For magnetic field strengths below 0.17 T the plasma has a more or less uniform radial distribution; above 0.17 T a contracted plasma column is present along the axis of the cylinder. In the symmetry plane between the two discharges measurements have been done on the rotational velocity of neutrals and ions, the electron density and temperature, the ion temperature, the plasma potential and the radial pressure distribution. The rotational velocity, the plasma potential and the pressure distribution are also calculated. The theoretical treatment is based on the theory developed by Klüber and Wilhelm and Hong. In the low magnetic field case velocities of 700 m/sec are found for ions as well as neutrals. The agreement between theory and experiment is good in this case. At high magnetic fields, the ions and neutrals are found to have azimuthal velocities of 1900 and 700 m/sec, respectively. The radial pressure enhancement due to the centrifugal forces is found to be approximately a factor of two whereas the theory predicts only a factor of 1.2. In a discharge in which a mixture of argon and xenon is used a relative separation factor of 2.15 is found.